1. Field of the Invention
The present invention generally relates to body framing systems for the assembly and welding of automobile bodies. More specifically, this invention relates to an automobile framing method and apparatus which enables the components of an automobile body to be loaded, positioned and welded in place, all within a single framing structure, such that the complexity of the assembly operation is reduced, and progressive series of positioning and welding operations are unnecessary.
2. Description of the Prior Art
In the manufacturing of automobiles and trucks, body frames, which typically consist of at least an underbody, a pair of aide frames, and front and rear headers, conventionally undergo a progressive series of positioning and welding steps before a structurally rigid body frame, termed a body-in-white, is produced. Though bodies are still manually assembled and welded, emphasis on automated assembly and welding operations has generated numerous automated and semi-automated framing systems.
Typically, framing systems which involve a degree of automation include the operations of (1) locating the components relative to each other on the underbody, (2) performing an initial pretack weld to "toy tab" the components together, (3) transporting the toy tabbed body to a "framing" welding station, (4) accurately establishing within a framing station the desired final geometry of all of the components of the body-in-white by laterally engaging the toy tabbed components with locating frames, often termed gate fixtures, (5) performing additional weld operations within the framing station to more permanently and securely weld the components together to accurately form the body-in-white, and then (6) transporting the body-in-white to a final welding, or respot, station where the remaining welds (the welds which, for whatever reason, could not be made in the framing station) are made to establish a structurally rigid body frame.
Though many variations of the above process are known, it is the general object of each framing system to accurately locate the body components relative to each other (establish a net location) and maintain the net location position throughout the later welding operations, until the structural rigidity of the body-in-white is sufficient to preserve the desired geometric configuration throughout the assembly line. A further object for most framing systems is to provide sufficient flexibility to accommodate more than one body style, so as to enhance the versatility of the assembly line and reduce the tooling cost per assembly unit.
As an illustration of the above, U.S. Pat. No. 4,162,387 to De Candia teaches a framing system which includes a framing station equipped with a transfer system for transporting a number of pallets through the framing station. Each pallet is equipped to support and locate an underbody subassembly which has been toy tabbed to apertures and various other body panels. Once at the framing station, the toy tabbed body is engaged with at least one pair of gate fixtures, each having clamps for holding the toy tabbed body so as to establish the final geometry of the body-in-white. More than two pairs of gate fixtures are present at the framing station, each pair being adapted to a particular body style. As a result, different body styles can be welded at the same framing station. Programmable robots are located at the framing station, each of which is provided with a welding gun to perform spot welding of the body-in-white, in accordance with the particular requirements of each different body style.
Since the programming robots must pass through the clamping frame, access to the body-in-white for welding all areas is limited and therefore this arrangement often results in the performance of only a portion of the required welds at the framing station and the partially welded subassembly of the body-in-white must be advanced to a second (respot) station where the final welding operation is performed. The respot station utilizes a different clamping frame to allow access of welding heads to the portions of the subassembly which could not be accessed in the first framing station. Therefore, respot operation is necessary with conventional framing systems because the gate fixtures and their associated transfer systems significantly limit access to the body-in-white within the framing station. In addition, the time required to operate the gate fixtures for each successive body-in-white, as well as the time required to interchange gate fixtures to accommodate different body styles, significantly reduces the amount of time within the assembly cycle which is available to perform the welding operation, while still sustaining a through-put rate compatible with prior and subsequent assembly operations.
Various attempts have been made to provide greater clearance to access the body-in-white in order to improve the efficiency of the welding operation and avoid a respot welding. For example, in U.S. Pat. No. 4,670,961, front and rear clamping frames are carried by rotary magazines located in position above the front and rear portions of the body-in-white. The clamping frames are located above the body-in-white and are pivotable to lower them into an operating position overlying the body-in-white in order to clamp the various panels associated with the welding operation. This arrangement does, indeed, provide more access from the sides to the various panels to be welded. However, the locating system described requires two independent clamping frames to be employed at opposite sides of the vehicle which necessitates that the two separate frames be independently located relative to the body and to each other. Clearly, this arrangement, although providing cleaner access, has some built-in inaccuracies in that the separate frames must be independently located relative to the body and to each other thereby resulting in additional tolerance limitations to be taken into consideration which affect the final tolerances of the assembled body. Also, this arrangement increases the potential for downtime of the assembly line as well as occupies significant floor space resulting in additional costs and slower cycle times.
Further attempts have been made to provide greater access to the body-in-white for welding by relocating the tooling which positions the body so that the tooling moves vertically and avoids any interference with the welding robots located on either side of the framing stations such as the example shown in Sciaky et al, U.S. Pat. No. 4,675,969.
From the above, it can be seen that a significant disadvantage with current framing systems is the requirement for successive welding operations as a result of the methods adopted to establish and preserve the final geometry of the body-in-white. Each successive welding operation not only requires its own dedicated welding guns, but also involves an entirely separate station on the factory floor, each of which occupies valuable floor space resulting in significant costs associated with tooling and plant facilities. Furthermore, successive framing and welding operations undesirably increase the overall cycle time for producing a body-in-white.
Another disadvantage with conventional framing systems is the toy tabbing operation noted above, in which the underbody and other body components are welded together to the extent necessary to position the components in relation to each other, so that the gate fixtures are subsequently capable of establishing the final geometry of the body-in-white. The toy tabbing operation may be automated to some degree, but typically results in a flexible structure which will collapse, or "match box", if not properly engaged by the gate fixtures. Furthermore, any geometric inaccuracies resulting from the toy tabbing process necessitates that, at the framing station, the gate fixtures must physically overwhelm the toy tabbed structure to precisely establish the desired geometry of the body-in-white.
A further disadvantage of conventional automated and semi-automated framing systems is the use of gate fixtures. The level of automation required with the use of gate fixtures complicates the layout and operation of the framing station, thus increasing the potential for downtime on the assembly line. Automated systems which are employed to selectively transfer gate fixtures to and from the framing station to accommodate different body styles occupy additional floor space, which further limits access to the body-in-white for welding, while also increasing the potential for downtime. Gate fixtures and their required accessories also limit the ability to use visual systems to analyze the geometry of the body-in-white prior to welding.
From the above discussion, it can be readily appreciated that the prior art does not disclose a framing system which separates the framing and welding operations into two distinct operations. Nor does the prior art teach a framing system by which the final geometry of a body-in-white can be established prior to welding, so as to avoid the use of gate fixtures during the welding operation. In addition, the prior art does not teach or suggest a framing system which entails the use of a single welding operation, so as to eliminate the conventional requirement for successive toy tabbing, welding and respot welding operations.
Accordingly, what is needed is a framing system which employs a framing device that enables a vehicle's body components to be accurately positioned and maintained relative to each other within the framing device, such that the entire framing device can be transported to a single framing/welding station at which all necessary welding can be performed on the body-in-white, whereby the framing system eliminates the practice of toy tabbing and respot welding, and eliminates the need for gate fixtures during the welding operation.